1. Field of the Invention
The present invention relates to an illuminating apparatus in which the light distribution can be controlled.
2. Description of the Related Art
In illuminating apparatuses to be installed outside, various light distribution characteristics are generally required depending on the installation environment. For example, with regard to an illuminating apparatus such as a tunnel lamp or a roadway lamp, different light distribution characteristics may be required for a travelling direction and a width direction of the roadway, and light distribution characteristics that are asymmetrical relative to the reference axis of light distribution may also be required within a specific plane (e.g., a vertical plane parallel to the width direction).
As a typical example in which these kind of light distribution characteristics are required, there is a case in which tunnel lamps on an expressway are installed on a wall surface of only one side of the tunnel (e.g., refer to Japanese Patent Application Laid-Open (JP-A) No. 2004-311259 (refer to FIGS. 3 to 5)). In general, tunnel lamps on an expressway are required to illuminate the road surface as well as a predetermined range (e.g., within a range of a certain height from the road surface) of the wall surface on both sides within the tunnel in order to reduce driver's anxiety and the like. In order to satisfy this requirement, tunnel lamps on an expressway are normally installed facing each other on both wall surfaces of the tunnel such that the wall surface on one side (as well as the road surface) is illuminated by the tunnel lamps installed on the other wall surface. However, it is preferable to install tunnel lamps on a wall surface of only one side of the tunnel in terms of the cost of the tunnel lamps and their wiring fixtures, the ease of maintenance, and the like. In response to such problems, in the invention disclosed in JP-A No. 2004-311259, the light distribution characteristics of the tunnel lamps in a vertical plane (cross-section of the tunnel) parallel to the road width direction are configured to be asymmetrical relative to the reference axis of light distribution, thereby illuminating the road surface as well as both wall surfaces within the tunnel so as to satisfy a predetermined illumination standard with tunnel lamps installed on the wall surface of one side.
FIG. 12 illustrates the light distribution characteristics of the illuminating apparatus disclosed in JP-A No. 2004-311259. In FIG. 12, light distributions a and b within two mutually orthogonal planes including a light distribution reference axis of the illuminating apparatus (hereinafter also referred to as “optical axis of the illuminating apparatus” or simply “optical axis”) C0 are indicated by a solid line and a dashed line, respectively. Herein, in FIG. 12, with regard to the angle around a photometric center O, the angle of the optical axis C0 is regarded as 0° and the counterclockwise direction is regarded as the positive direction.
As illustrated in FIG. 12, the light distribution a has peaks in both the positive and negative angular directions, and exhibits an asymmetrical distribution relative to the optical axis C0. Thus, in this light distribution, the distribution profile of a distribution A having a peak in the negative angular direction is different from that of a distribution B having a peak in the positive angular direction. In particular, the absolute value of the angle at which the peak occurs and the light intensity at the peak are different in each of the distributions A and B.
When using an illuminating apparatus having such light distribution characteristics as tunnel lamps installed on the wall surface of one side within a tunnel, a plane including the light distribution a illustrated in FIG. 12 corresponds to a vertical plane that is parallel to the width direction of the roadway. Further, the light distribution characteristics of the illuminating apparatus are adjusted according to the predetermined installation position, installation angle, and the like of the illuminating apparatus such that a predetermined range of the side wall on the side on which the illuminating apparatus is installed is illuminated by illumination light corresponding to the distribution A of the light distribution a, and a predetermined range of the side wall on the opposite side with the roadway therebetween is illuminated by illumination light corresponding to the distribution B of the light distribution a which is brighter than the distribution A. Thereby, the road surface as well as both side walls within the tunnel can be illuminated so as to satisfy a predetermined illumination standard.
JP-A No. 2004-311259 discloses the following as an illuminating apparatus having the above-described light distribution characteristics: an illuminating apparatus 100 including a straight tube-shaped fluorescent lamp 110 and a reflecting member 112 disposed on the rear side of the fluorescent lamp 110 (refer to FIG. 13). The reflecting member 112 is formed to have an inverse U-shaped cross-section by connecting a first and a second reflecting panel 113 and 114, whose reflecting surfaces are constituted by a single curved surface, to each other in a continuously integral manner at one end side thereof. Illumination light corresponding to the distribution A is generated when the first reflecting panel 113 reflects light from the fluorescent lamp 110, whereas illumination light corresponding to the distribution B which is brighter than the distribution A is generated when the second reflecting panel 114, whose reflecting surface is larger than the reflecting surface of the first reflecting panel 113, reflects light from the fluorescent lamp 110.